I think Rapids Riders is more MN focused, but they take trips to rivers in WI. The WI boating website is Badger State Boating Society
(stands for Badger State Boating Society). Granted, BSBS is basically dead right now.
If you are looking for good whitewater close to Madison, you are basically out of luck. All of the good/decent rivers are in Northern WI at least a 2.5hr+ drive away. You should check out the American Whitewater pages for the Red River, Wolf River, Peshtigo River, Menominee River, Pike River, etc...They are all WI classics. There is also a decent dam released whitewater playpark/slalom course in Wausau, WI. There is a recreational release at Wausau this coming weekend. You will find TONS of other boaters at Wausau releases.
If you want additional info just PM me